We investigate temperature-and composition-dependent structural and
dynamical properties of Al-Au melts. Experiments are performed to obtain
accurate density and viscosity data. The system shows a strong negative
excess volume, similar to other Al-based binary alloys. We develop a
molecular-dynamics (MD) model of the melt based on the embedded-atom
method (EAM), gauged against the available experimental liquid-state
data. A rescaling of previous EAM potentials for solid-state Au and Al
improves the quantitative agreement with experimental data in the melt.
In the MD simulation, the admixture of Au to Al can be interpreted as
causing a local compression of the less dense Al system, driven by less
soft Au-Au interactions. This local compression provides a microscopic
mechanism explaining the strong negative excess volume of the melt. We
further discuss the concentration dependence of self-and interdiffusion
and viscosity in the MD model. Al atoms are more mobile than Au, and
their increased mobility is linked to a lower viscosity of the melt.